Compact electrically steerable tracking antenna feed system

ABSTRACT

Described is an electrically steerable tracking antenna feed system employing a pair of ferrite phase shifters, one of which produces positive phase shift and the other of which produces negative phase shift with increasing applied magnetic field. The ferrite phase shifters, arranged in side-by-side relationship in a bifurcated wave guide, are surrounded by a common electromagnet.

United States Patent [72] inventor Appi. No. Filed Patented Assignee[54] COMPACT ELECTRICALLY STEERABLE TRACKING ANTENNAFEED SYSTEM 6Claims, 4 Drawing Figs.

[52] US. Cl 343/778, 343/78 1 343/854, 333/241 [51] InLCl ..H01q 13/00[50] Field oiseflrch 343/778. 781, 787, 353, 854

Ssolt $$Q v Primary Examiner- Eli Lieberman Atlorneys- F. H. Henson andE. P. Klipfei- ABSTRACT: Described is an eiectricaiily steerabietracking antenna feed system employing a pair ofiferrite phase shifters,one of which produces positive phase shift and the other of whichproduces negative phase shift with increasing applied magnetic field.The ferrite phase shifters, arranged in side-byside relationship in abifurcated wave guide, are surrounded by a common eiectromagnet.

PATENIED urn/2 197:

23 CONTROL CIRCUIT K m 3 V mC L E N A D ATTORNIEY COMPACT ELECTRICALLYSTIEEIKAIBLIE TRACKING ANTENNA FEED SYSTEM BACKGROUND OF THE INVENTIONAs is known, longitudinally magnetized reciprocal ferrite phase shiftersshow anomalous behavior in that some show increasing phase shift withincreasing applied field while others show decreasing phase shift withincreasing applied field. In this respect, there are two competingmechanisms which govern the type of phase shift. These can be termedr-effective and suppressed Faraday rotation. The latter sets in when theguide is thick enough to support a cross-polarized electric field of thesame order of magnitude as the incident electric field and results inincreasing phase shift with increasing applied field. The uAeffectivemechanism, on the other hand, results when the guide is of suchthickness that it will not support a cross-polarized electric field ofthe same order of magnitude as the incident electric field and resultsin decreasing phase shift with increased applied magnetic field.

SUMMARY OF THE INVENTION As an overall object, the present inventionseeks to provide a new and improved electrically steerable trackingantenna feed system employing ferritephase-shifting devices, at leastone of which will produce an increasing negative phase shift withincreasing applied magnetic field and the other of which will produce anincreasing positive phase shift with increasing applied magnetic field.

More specifically, an object of the invention is to provide anelectrically steerable tracking antenna feed system of the typedescribed wherein the ferrite phase shifters are arranged inside-by-side relationship in a bifurcated waveguide and surrounded by acommon magnetizing coil.

in accordance with the invention, an electrically steerable trackingantenna feed system is provided comprising at least one pair ofantennas, a waveguide having one end adapted for connection to a sourceof wave energy for both of said antennas, a wall dividing the waveguideinto two separate wave energy transmission paths, one of which is widerthan the other, and ferrite slabs in the respective wave energytransmission paths, one slab being wider than the other.

A common magnetic coil surrounds both of the wave energy transmissionpaths to produce a magnetic field extending along the axis of thewaveguide. With this arrangement, and assuming that the thickness of thewider slab is great enough to support a cross-polarized electric fieldof the same order of magnitude as the incident electric field while thethinner slab is not, the phase shift experienced by the wave energy inpassing through the thin ferrite slab will decrease with appliedmagnetic field; while the passing through the wide ferrite slab willincrease with applied field. The system is completed by connecting therespective wave energy transmission paths to two antennas which arespaced apart such that upon variation of the magnetic field applied toboth ferrite slabs, the composite radiation pattern produced by theantennas will be caused to scan back and forth.

Further, in accordance with the invention, the wave energy in separateferrite-filled transmission paths, having experienced different phaseshifts, may be further divided into portions which pass through thickand thin ferrite slabs, under the influence of an axial magnetic field,for the purpose of producing four or more separate antenna feeds.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings which form a part of this specification,and in which:

FIG. I is a cross-sectional schematic view of one embodiment of theinvention for feeding two separate antenna elements;

FIG. 2 is a schematic illustration of another embodiment of theinvention for feeding four separate antenna elements;

FIG. 3 is a cross-sectional view of a system in accordance with theinvention for providing single-axis scanning employing a Cassegrainantenna feed; and

FIG. 4 illustrates the manner in which the device of FIG. 3 is employed.

With reference now to the drawings, and particularly to FIG. I, thesystem shown includes a waveguide 10 having an inner wall 12 whichdivides it into two parallel wave energy transmission paths M and 16.The wave energy path 14, it will be noted, is much thinner than the path16. Both path 14 and path 16 are filled with ferrite slabs l8 and 20,the slab 18 being much thinner than slab 26. Both slabs 18 and 20 aresurrounded by an electromagnetic coil 22 connected to a control circuit23 and adapted to produce an axial magnetic field along the length ofthe waveguide 10. The wall 12 separating the two wave energy paths isclosely adjacent the top wall in waveguide Ill as shown in FIG. I but isbent inwardly as it passes through matching transformers 24 and 26 untilit assumes a central position where it divides the wave energy passingthrough the waveguide 10. Similarly, the other end of the wall 12 isbent inwardly as it passes through matching transformers 28 and 30 untilit assumes a central position. At this point, the center wall isconnected, as a common wall, to two waveguide sections 32 and 34 whichare, in turn, connected to antennas 36 and 38, respectively.

As was mentioned above, when the waveguide section within which theferrite slab is disposed is thick enough to support a cross-polarizedelectric field of the same order of magnitude as the incident electricfield, phase shift occurs by virtue of "suppressed Faraday rotation," inwhich case the phase shift experienced by the wave energy in passingthrough the ferrite increases with increased applied magnetic field.This is the case with the ferrite slab 26. On the other hand, when theslab is not thick enough to support a cross-polarized electric field ofthe same order of magnitude as the incident electrical field, the phaseshift decreases as the applied magnetic field increases. This is thecase with the ferrite slab 18. Hence, as the magnetic field applied bythe coil 22 increases, the phase shift experienced by the wave energy inpassing through ferrite slab 18 will decrease while that experienced inpassing through slab 20 will increase. The result is that the waveenergy applied to the two antennas 36 and 38 will always be out ofphase; and as the applied magnetic field is varied, so also will be thephases of the energy applied to the antennas 36 and 38 to cause thecomposite radiated beam to scan back and forth.

In FIG. 2 another embodiment of the invention is shown wherein waveenergy is fed to four antennas 40-46. In this case, the wave energy isdivided into two parallel paths and passed through two slabs 48 and 50,the thinner ferrite slab causing a negative phase shift and the thickerslab 48 causing a positive phase shift. The wave energy which hasexperienced a positive phase shift in passing through slab 48 is thenfed into a second bifurcated ferrite phase shifter comprising a thinferrite slab 52 and a relatively wide slab 54. The wave energy fromslabs 52 and 54 is then applied to the antennas 44 and 46, respectively.

The same is true of the wave energy which experienced a negative phaseshift in passing through slab 50, Le, it is passed through a secondbifurcated chamber having a thin ferrite slab 56 in side-by-siderelationship with a relatively wide slab 58. Wave energy passing throughslab 56 is applied to antenna 40; while that passing through slab 58 isapplied to antenna element 42. In this manner, various scanning arraysor radiation patterns can be achieved from the antennas 40-46 which neednot be arranged in line as shown in FIG. 2.

In FIGS. 3 and 4, another embodiment of the invention is shown in whichelements corresponding to those shown in FIG. l. are identified bycorresponding reference numerals. In this case, however, the waveenergy, after passing through matching transformers 28 and 30, is fedthrough a split feedhorn 60 and then reflected from a reflector 62 backonto a parabolic dish 64. The wave energy fed to one side of the dish 64is, of course, out of phase with respect to that fed onto the otherside; and the two signals combine to produce a directional effect whichwill cause scanning of the beam when the magnetic field applied by thecoil 22. is varied.

The device shown in FIG. ll can also be used as a microwave switch oramplitude modulator. In switching, the phase-shifting elements 18 and 20go between +-90 relative phase shift and :90", switching the energybetween the two output ports. For modulation, one output port can beterminated while the other port receives the modulated wave. Modulationis achieved by varying continuously the phase at the two ports betweenzero relative phase shift and :90 relative phase shift.

Although the invention has been shown in connection with certainspecific embodiments, it will be readily apparent to those skilled inthe art that various changes in form and arrangement of parts may bemade to suit requirements without departing from the spirit and scope ofthe invention.

I claim as my invention:

1. In an electrically steerable tracking antenna feed system, thecombination of a pair of antennas, a waveguide having one end adaptedfor connection to a source of wave energy for both of said antennas, awall dividing said waveguide into two separate wave energy transmissionpaths one of which is wider than the other, ferrite slabs in saidseparate wave energy transmission paths, one slab being wider than theother, a common magnetic coil surrounding both of said wave energytransmission paths to produce a magnetic field extending along the axisof said waveguide, one of said ferrite slabs producing increasingpositive phase shift as said magnetic field is increased and the otherof said ferrite slabs producing increasing negative phase shift as saidmagnetic field is increased, first antenna means connected to one ofsaid wave energy transmission paths, and second antenna means connectedto the other of said wave energy transmission paths.

2. The tracking antenna feed system of claim 1 wherein said wide slabproduces increasing positive phase shift as said magnetic field isincreased and said narrow slab produces increasing negative phase shiftas said magnetic field is increased.

3. The tracking antenna feed system of claim 1 including matchingtransformer means at opposite ends of said ferrite slabs.

4. The tracking antenna feed system of claim 1 wherein said first andsecond antenna means each comprise a plurality of antennas, and ferritephase-shifting devices interposed between each of said first and secondantenna means and said narrow and wide ferrite slabs.

5. The tracking antenna feed system of claim 4 wherein saidlatter-mentioned ferrite phase-shifting devices comprise ferrite slabsin a bifurcated waveguide divided into wide and narrow wave energypaths.

6. The tracking antenna feed system of claim 1 wherein said first andsecond antenna means comprise devices for feeding wave energy toopposite sides of an antenna reflector in a Cassegrain antenna feedsystem.

a a a a:

1. In an electrically steerable tracking antenna feed system, thecombination of a pair of antennas, a waveguide having one end adaptedfor connection to a source of wave energy for both of said antennas, awall dividing said waveguide into two separate wave energy transmissionpaths one of which is wider than the other, ferrite slabs in saidseparate wave energy transmission paths, one slab being wider than theother, a common magnetic coil surrounding both of said wave energytransmission paths to produce a magnetic field extending along the axisof said waveguide, one of said ferrite slabs producing increasingpositive phase shift as said magnetic field is increased and the otherof said ferrite slabs producing increasing negative phase shift as saidmagnetic field is increased, first antenna means connected to one ofsaid wave energy transmission paths, and second antenna means connectedto the other of said wave energy transmission paths.
 2. The trackingantenna feed system of claim 1 wherein said wide slab producesincreasing positive phase shift as said magnetic field is increased andsaid narrow slab produces increasing negative phase shift as saidmagnetic field is increased.
 3. The tracking antenna feed system ofclaim 1 including matching transformer means at opposite ends of saidferrite slabs.
 4. The tracking antenna feed system of claim 1 whereinsaid first and second antenna means each comprise a plurality ofantennas, and ferrite phase-shifting devices interposed between each ofsaid first and second antenna means and said narrow and wide ferriteslabs.
 5. The tracking antenna feed system of claim 4 wherein saidlatter-mentioned ferrite phase-shifting devices comprise ferrite slabsin a bifurcated waveguide divided into wide and narrow wave energypaths.
 6. The tracking antenna feed system of claim 1 wherein said firstand second antenNa means comprise devices for feeding wave energy toopposite sides of an antenna reflector in a Cassegrain antenna feedsystem.